NZ588233A

NZ588233A - Dynamically adjusting a compensation term based on a stored profile for a motor

Info

Publication number: NZ588233A
Application number: NZ588233A
Authority: NZ
Inventors: Warren Gordon Pettigrew; Ian Palmer
Original assignee: Dynamic Controls
Priority date: 2010-09-28
Filing date: 2010-09-28
Publication date: 2011-06-30
Also published as: US9257926B2; EP2522070A4; EP2522070B1; WO2012044182A1; EP2522070A1; US20130035816A1

Abstract

Disclosed is a method of controlling at least one motor in a motorised mobility vehicle, where the motor is part of a drive circuit for mobilising the vehicle. The method includes utilising a stored profile of a motor performance parameter to develop a compensation term for controlling the motor, and dynamically updating the compensation term when the vehicle is in use. The stored profile is of a resistance based variable associated with the motor as a function of a further variable.

Description

<div class="application article clearfix" id="description"> Received at IPONZ 6 December 2010 Our Ref: DYN037 Patents Form No. 5 PATENTS ACT 1953 COMPLETE SPECIFICATION AN IMPROVED METHOD AND CONTROL SYSTEM FOR CONTROLLING MOBILITY VEHICLES We, Dynamic Controls, a New Zealand company of 17 Print Place, Riccarton, Christchurch, New Zealand, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: 1 Received at IPONZ 6 December 2010 2 AN IMPROVED METHOD AND CONTROL SYSTEM FOR CONTROLLING MOBILITY VEHICLES FIELD OF THE INVENTION 5 The present invention relates to an improved method and control system for controlling mobility vehicles. In particular, the present invention relates to an improved method and control system for controlling at least one electric motor of a mobility vehicle using motor profiles. 10 BACKGROUND It is important that motor drive systems in mobility vehicles are carefully controlled to avoid placing the user of the vehicles in danger and/or harming 15 others around them, or at the very least to provide a stable and reliable driving experience. The mobility vehicles may be, for example, motorized wheelchairs or scooters that assist users in being mobile. The motor drive systems of these vehicles incorporate various different forms of motor control which aim to provide the user with reliable and safe operation of the vehicle. 20 One problem associated with motor drive systems that incorporate permanent magnet or shunt wound motors is that changes in the armature resistance of the motors can cause changes in the speed of the mobility vehicle when the loading varies. 25 One form of control system used in mobility vehicles to compensate for the armature resistance effect is known as IXR load compensation. This traditional approach measures the load induced current of the drive motors and applies an extra voltage to compensate for the voltage lost across the motor armature 30 resistance. This technique is termed IXR load compensation. This compensation method works throughout all four control quadrants of the mobility vehicle so that, not only will the motor hold speed during positive loading, it will also hold speed during negative loading or braking. The four control quadrants are forward drive, reverse braking, forward braking and reverse drive. Received at IPONZ 6 December 2010 3 However, because of resistance effects, these motors may operate more slowly with imposed positive loading. Therefore, where tight speed regulation is important, as with drive systems for power wheelchairs and mobility scooters, 5 some means of compensating for load induced speed changes is desirable. One such area where this is particularly relevant is that of mobility vehicles (such as power wheelchairs, for example) that use differential steering via two traction motors where steer precision is directly dependant on the speed holding ability of the motors. 10 The load compensation on these motors is not currently performed accurately because motor resistance is a variable and is a function of current, temperature, speed and time. If these inaccuracies lead to over-compensation, harsh and unstable driving characteristics may result. If under-compensated, driving 15 precision may be compromised. Therefore, because of risks associated with over-compensation, it is generally required that under-compensation is performed. Further, mobility vehicles traditionally need programming tools to adjust the level 20 of compensation. For example, the level of compensation is adjusted only when the vehicle is taken in for a service. One method of measuring motor resistance at stall is described in US patent application US 2010/0007299. However, this system requires the motor not to be 25 turning when the measurement is taken, which can result in inaccurate and varying measurements of resistance due to the large number of different positions in which the motor may stop. Further, this single resistance measurement remains fixed when the mobility vehicle is in use. 30 Another known method of compensating for motor resistance is described in US patent US 4,266,168. This describes a method of measuring the back EMF of a motor during use of the motor to generate a feedback signal that accounts for the motor's resistance. However, once measured, the feedback signal is only Received at IPONZ 6 December 2010 4 updated periodically resulting in a fixed feedback resistance value being applied between updates. A further known problem with motor control in mobility vehicles is that of 5 monitoring and detecting potential scenarios associated with a motor before they occur and reducing the potential for these scenarios to occur. In general, known systems that attempt to detect specific scenarios are complex and expensive. These scenarios may include, for example, potential damage to the motor, loss of performance, service requirements, etc. 10 For example, in a DC brush motor, problems may occur as the motor gets older when the brushes on the commutator start to wear. The brush damage can cause an increase in motor electrical resistance, thus requiring additional current to operate the motor resulting in overheating of the motor. 15 Service scheduling of mobility vehicles is generally done by way of allocating a fixed period in between services. This can lead to increased damage to the motor components if wear and tear on the motor occurs rapidly in between services. Further, as wear and tear occurs in between services, the operation of 20 the mobility vehicle may become erratic and unsafe. Monitoring of motor temperature to prevent damage is generally performed by applying temperature sensors and sensing circuitry. However, this added circuitry and extra components increase cost and complexity. 25 An object of the present invention is to provide an improved method and control system for mitigating the effects of motor characteristics on the operation of a mobility vehicle. 30 A further object of the present invention is to provide an improved method and control system for updating a motor characteristic profile. Received at IPONZ 6 December 2010 5 A further object of the present invention is to provide a method of detecting the likelihood of potential scenarios with a motor and providing an indication of these scenarios. 5 A further object of the present invention is to provide an improved method and system for controlling power applied to a motor dependent on one or more of the motor's performance characteristics. A further object of the present invention is to provide an improved method and system for monitoring a motor based on one or more of the motor's performance 10 characteristics. Each object is to be read disjunctively with the object of at least providing the public with a useful choice. 15 The present invention aims to overcome, or at least alleviate, some or all of the afore-mentioned problems. SUMMARY OF THE INVENTION 20 It is acknowledged that the terms "comprise", "comprises" and "comprising" may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, these terms are intended to have an inclusive meaning - i.e. they will be taken to mean an inclusion of the listed components which the use directly references, 25 and possibly also of other non-specified components or elements. According to one aspect, the present invention provides a method of controlling at least one motor in a motorised mobility vehicle, wherein the motor is part of a drive circuit for mobilising the mobility vehicle, the method including the steps of: 30 utilising a stored profile of a motor performance parameter to develop a compensation term for controlling the motor, wherein the stored profile is of a resistance based variable associated with the motor as a function of a further variable and dynamically updating the compensation term when the mobility vehicle is in use. Received at IPONZ 6 December 2010 6 According to yet a further aspect, the present invention provides a control system in a motorised mobility vehicle, the control system arranged to control at least one motor wherein the motor is part of a drive circuit for mobilising the mobility 5 vehicle, the control system including: a compensation term development module arranged to utilise a stored profile of a motor performance parameter to develop a compensation term for controlling the motor, wherein the stored profile is of a resistance based variable associated with the motor as a function of a further variable and 10 dynamically update the compensation term when the mobility vehicle is in use. BRIEF DESCRIPTION OF THE DRAWINGS 15 Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows system conceptual block diagram according to an embodiment of the present invention; 20 Figure 2 shows a first parameter plot; Figure 3 shows a second parameter plot; Figure 4 shows a DC motor equivalent circuit; Figures 5A and 5B show block functional diagrams according to an embodiment of the present invention; 25 Figure 6 shows a performance parameter profile according to an embodiment of the present invention; Figure 7 shows a functional block diagram according to an embodiment of the present invention; Figures 8A and 8B show block functional diagrams according to an embodiment 30 of the present invention. DETAILED DESCRIPTION OF THE INVENTION First Embodiment 35 Received at IPONZ 6 December 2010 7 The following embodiment describes a control system and method of controlling a mobility vehicle. The mobility vehicle may be, for example, a motorised wheelchair or motorised scooter. 5 The mobility vehicle includes a drive system that has two DC drive motors for mobilising the vehicle. It will be understood that, as an alternative, the mobility vehicle may have one or more drive motors. According to this embodiment, the DC drive motors are DC brush motors. It will 10 be understood that, as an alternative, the DC drive motors may be any suitable type of permanent magnet or shunt wound motor where load changes result in speed changes due to armature resistance, and where the back EMF (electromotive force) is directly proportional to the rotational speed of the motor. Further, the mobility vehicle may use a combination of different drive motors. 15 According to this embodiment, a method and associated control system is described that develops a compensation term used to control the operation of the two drive motors forming the differential drive circuit of the mobility vehicle. 20 Figure 1 shows a system conceptual block diagram of various modules and functions used according to this method. A controller 1 includes all the control components forming the control system of the mobility vehicle. The modules and functions shown in figure 1 and described below relate to a 25 single motor 2. However, it will be understood that these modules and functions may be duplicated for each of the motors (such as motor 3) in the mobility vehicle drive system. A first motor 2 is connected to a first motor bridge 4. A second motor bridge 5 is 30 connected to the second motor 3. A bridge driver 6 is used to drive the first motor bridge 4. Forming part of a microcontroller 9 are an error amplifier function 7, a differential amplifier function 8 and a steering and speed processor 10. It will be understood Received at IPONZ 6 December 2010 8 that the error amplifier function and amplifier function may also be implemented using any suitable module, software and/or circuit arrangement. The steering and speed processor 10 receives input signals from a joystick 11 in the form of a steering signal 12 and a speed signal 13. The steering signal relates to the 5 direction in which the mobility vehicle has been instructed to travel by the user. For example, by pushing the joystick to the left, the right side motor (e.g. motor 2) and left side motor (e.g. motor 3) are sent drive signals which cause the right side motor to turn faster than the left side motor. This then causes the mobility vehicle to turn left. 10 The speed signal relates to the speed the mobility vehicle has been instructed to travel by the user. For example, by pushing the joystick in a forward position, the speed of both motors is increased. 15 The steering and speed processor output includes an inhibit signal 14, which is fed to the bridge driver 6. This inhibit signal 14 causes the power to the motors (2, 3) via the bridges (4, 5) to be reduced. The steering and speed processor output also includes a motor speed command signal 15 for controlling the first motor 2 via the error amplifier 7, the bridge driver 6 and the bridge 4. 20 The differential amplifier 8 develops a difference signal based on the terminal voltages of the motor 2. The error amplifier 7 develops a control signal based on the motor speed command signal 15, the output of the difference amplifier 8 and the current provided by a current sensor 16, which detects the current being 25 applied to the motor 2. Power is provided to the motors and control system by way of a battery 19. Although not shown in figure 1, it will be understood that further components are 30 used to control the second motor 3 in a similar manner to the method used to control the first motor 2. That is, the circuit includes a second bridge driver, error amplifier, difference amplifier and current sensor to control the operation of the second motor 3 via the second bridge 5. Further, it will be understood that the Received at IPONZ 6 December 2010 steering speed processor 10 includes a further motor speed control signal and further inhibit signal for controlling the second motor via the second bridge 5. As explained above, in this embodiment the DC motors are DC brush motors. 5 Brush resistance contributes significantly to motor resistance. Additionally the contact resistance of the brush onto the commutator has a high dependency on current, temperature and wiping speed. If the wiping speed is zero, the resistance varies greatly with the degree of contact at the time of measurement as depicted in Figure 2. 10 Overlaying the issue of wiping speed, it can also be seen that the motor resistance is a complex function of current. This arises from the fact that the brushes make contact with the metal commutator at minute points. The current density at these points is very high which makes the brushes heat. Carbon 15 brushes have a negative temperature coefficient of resistance so the resistance effectively drops with increasing current. It is not uncommon for the resistance to vary by a factor of 3:1. This means that motor compensation can have a 3:1 error in compensation if the resistance is not taking account of properly. 20 It has also been determined that, provided the wiping speed of the brush motor is greater than a few millimetres per second, the- resistance becomes stable. Therefore, it is preferable to measure the resistance of the motor when the motor is running. 25 Another variable is that of overall motor temperature. This also has a complex and dramatic effect on motor resistance as depicted in Figure 3. As a first step, a performance parameter profile is created. According to this embodiment, the performance parameter is a resistance-based parameter. The 30 profile is created by measuring the terminal voltage and back EMF of the motor at different load currents. Therefore, using the relationship of: R = (V-e) / i Received at IPONZ 6 December 2010 10 where R = electrical resistance of the motor, V = terminal voltage of the motor, e = back EMF of the motor and I = load current, a value for R can be determined at various load currents. The calculated R value is the momentary motor resistance for the conditions of current, speed and temperature at the time of the sample 5 being taken. A simplified DC motor equivalent circuit is shown in Figure 4 to explain how R = (¥ - e)/l. It will be understood that it is not necessary to use the actual resistance value R directly for the profile and that any related resistance-based variable or 10 calculation may be used that is associated with R. For example, a ratio of R x I (i.e. a voltage value) or (V-e)/R (a current value) may be stored as an alternative, where the values are all based on the measured electrical resistance of the motor. 15 According to this embodiment, the determined R values for specific current values are stored in a table and values of R in between the measured current values are interpolated and stored. Alternatively, it will be understood that a best fit equation may be determined based on the measured R values. 20 Various components shown in figure 1 are used to develop the motor profile. The current sensor 16 is used to develop the load current value I. The difference amplifier function 8 is used to develop the terminal voltage V, and the back EMF voltage e. 25 Figure 5A shows a block functional diagram of how the V, I and e values are used to develop the profile. The V, I and e values are provided to a profile development module 501. The profile development module includes a profile development logic module 503 and a storage module 505. The V, I and e values are input to the logic module 503 to determine the R value based on the equation 30 R= (V-e)/l. The logic module 503 outputs the R value to the storage module 505, where the R value is stored for different I values. For example, the values for R for varying I values are stored as a look up table. Received at IPONZ 6 December 2010 11 Figure 5B shows an alternative block functional diagram of how the V, I and e values may be used to develop the profile. The system includes the same components as described above in relation to figure 5A. In addition, the profile 5 development module 501 includes an equation development module 509 that reads the stored R values and associated I values to develop a best fit equation. Figure 6 shows an example of a resistance based profile of electrical resistance against load current for a motor. 10 According to this embodiment, only forward driving currents are recorded and reverse currents are developed by mirroring the forward current values. Alternatively, a full range of forward and reverse current values may be developed for the profile. 15 Generally the lower part of the working current range of a motor has greater variability with current so is generally considered more important to plot. Therefore, a greater resolution of load current values may be recorded in the lower portion of the working current range to provide a more accurate profile. 20 Further, resistance measurements in braking can be assumed to be equal to those in drive. Therefore, the resistance map for quadrant 1 (driving forward) in this embodiment is considered the same as the other 3 quadrants. Alternatively, the profile may be developed by taking measurements of R and I in all 4 25 operating quadrants of the motor. According to this embodiment, a profile is created for each motor. However, it will be understood that, as an alternative, a single profile may be created from a single motor and used for all motors of a similar construction. 30 To calculate R, the load current is developed as follows. The load current is sampled using the load current sensor 16. It will be understood that, as an alternative, the load current may be determined using other suitable methods. Received at IPONZ 6 December 2010 12 To calculate R, the terminal voltage is developed as follows. According to this embodiment, the terminal voltage is a PWM (Pulse Width Modulated) waveform. The terminal voltage reading is therefore established by filtering or by calculation after measuring the mean peak voltage and the PWM ratio. 5 To calculate R, the back EMF is developed as follows. The drive to the motor is momentarily turned off to let the motor free-wheel for a few milliseconds. This allows the back EMF to be established. As soon as the motor back EMF is established, it is sampled and recorded. Just prior to the back EMF being 10 sampled, the motor current and terminal voltage are sampled as described above. Initially, the resistance based profile may be loaded Into the controllers manually during product assembly or commissioning. 15 An automated process is provided that updates the table repeatedly to accommodate for resistance changes due to motor heating and aging. This updating process may be performed automatically during routine driving, and preferably without the user being made aware that the profile update is 20 happening. By doing this, each individual motor can be separately compensated so that motor to motor variations are seamlessly accommodated throughout the life of the motor. When the control system is turned off (generally for a few milliseconds) to sample 25 the back EMF an audible click may be heard or a small torque pulse felt. In order to minimize these effects it is preferable that sampling is not done under conditions of very high loading and it is preferable that the motor drive is turned off for a period just long enough to establish a stable back EMF voltage. This period may depend on actual operating conditions, on a predetermined time 30 period or a stored algorithm. Alternatively, the profile may be updated during servicing of the vehicle. Received at IPONZ 6 December 2010 13 Referring back to figure 5A the block functional diagram shows how the compensation term is developed. A compensation term module 507 retrieves Rf(I) values (i.e. Rasa function of 5 current) from the storage module 505 based on the monitored I value being received and outputs the relevant Rf(l) value as a profile term. The profile term (R) is fed to a multiplier along with the monitored I value within the compensation term module to create a compensation term IXR. The compensation term IXR is added to the Voltage drive signal (V drive) to provide a drive signal to the 10 switching bridge 4 to apply motor voltage in proportion to V drive and to apply additional voltage to compensate for the loss of voltage across the resistance of the motor. Alternatively, as shown in figure 5B the compensation term may be developed i 5 based on the best fit equation. The profile term R, and so the compensation term IXR, are dynamically updated based on the developed load current value (I). It is preferable that the profile term and compensation term are continuously updated without providing a 20 substantial break in between updates. As the motor current commonly changes by orders of magnitude in a millisecond time-frame, according to this embodiment the compensation term is dynamically applied in a millisecond time frame in order to continuously and accurately 25 compensate for motor resistance. However, it will be understood that different time frames for applying the compensation term dynamically may be used. It is preferred that the load current is monitored in real time and that the compensation term is developed in real time. 30 It is also preferred that the stored profile is shaped by current, and that the compensation term is shaped by the stored profile. Received at IPONZ 6 December 2010 14 With any feedback control system some form of stabilization is necessary generally in the form of a proportional-integral term. The closer the system becomes to 100% compensated, the more critical stabilization becomes. Therefore, according to this embodiment, the compensation term includes both a 5 proportional arid integral profile term. However, it will be understood that, as an alternative, the compensation term may only include a proportional term, or may include a proportional, integral and derivative term. Therefore, the compensation term generated using the above described circuit 10 shown in figure 1 is based on one or more performance parameters of the motor. Optionally different profiles may be developed for the motor based on the speed of operation. Therefore, the control system may monitor the speed of the mobility vehicle and use this extra variable to determine which of the stored resistance 15 based profiles are to be used. This therefore enables the IXR compensation term to be optimized for different driving speeds. According to this embodiment, the motor resistance is 100% compensated so that there is no change of speed with loading. However, it will be understood 20 that, in some circumstances, it may be beneficial to apply less than 100% compensation to assure smoothness or give some "feel" to the drive of the mobility vehicle. For example when approaching an incline, a slight reduction in speed due to the reduced compensation provides an expected driving experience, which re-assures the operator of the vehicle. 25 Optionally, changes in resistance beyond the expected norm may be recorded by the system. For example, the expected norms could be programmable numbers entered by the chair manufacturer. Changes beyond the expected norm may indicate that a service, such as a brush change, is due or that the motor has 30 become over-heated. A warning may be generated by the system to alert the operator of the vehicle. Alternatively, an automatic power limiting routine may be instigated by the controller to limit possible motor damage. Further, a log of dynamic motor resistance may be stored in the controller for downloading during service to enable the service entity to evaluate the state of the motors. This Received at IPONZ 6 December 2010 15 information would be valuable for service personnel for fault-finding and for predicting motor service such as brush changing. As shown in figure 3, the electrical resistance of the motor varies with respect to 5 the temperature of the motor. Therefore, using this relationship it is possible to determine a range of resistance values that are associated with a preferred operating temperature. By dynamically monitoring the resistance value of the motor, a percentage increase in the resistance value may be monitored, stored or recorded. 10 Where the percentage increase has exceeded a predetermined threshold value, a warning signal may be developed. For example, the warning signal may be a visible or audible signal to make the user aware that the motor is overheating and so they should slow the vehicle down. Alternatively, the warning signal may be 15 generated and stored so that service engineers may be made aware of the over temperature warnings when the vehicle is being serviced. Alternatively, where the percentage increase has exceeded a predetermined threshold value, the power being supplied to the motor may be limited to 20 automatically reduce the temperature of the motor. For example, the power to the motor may be limited by adjusting a limiting or compensation term that is applied to the control system to control the operation of the motor. Further, trends in the R values being monitored may be recorded or stored. 25 These trend values may then be reviewed by the user to predict when a service schedule is due. Alternatively, the system may automatically predict when a service schedule is due and provide a visible or audible warning to the user to that effect. For example, if the system detects that the resistance value has increased by 20% over a predefined period, such as a month for example, the 30 system may issue a warning that the mobility vehicle will require a service within a month. As a further example, if the system detects that the resistance value has increased by 30% over a predefined period, such as a month for example, the system may issue a warning that the mobility vehicle should have a service immediately. Received at IPONZ 6 December 2010 16 Also, by monitoring the electrical resistance values, if the system detects that the resistance value has exceeded a predefined threshold value, a warning signal may be generated. For example, the warning signal may be a visible or audible 5 signal to make the user aware that a fault has developed and requires attention. Figure 7 shows a functional block diagram of components that may be used to detect operational scenarios associated with the resistance based profile of the motor. 10 The resistance based profile stored in the storage module 505 is monitored by a profile monitoring module 701. A scenario prediction module 703 is arranged to predict an operation scenario based on the output received from the profile monitoring module 701. An output module 705 is arranged to provide an output 15 707 based on the predicted operation scenario, where the operation scenarios are as described above in relation to the resistance based performance parameters of the motor. Figures 8A and 8B show further embodiments of the present invention in the form 20 of block functional diagrams. Figure 8A shows a block functional diagram of a motor performance monitoring system which is arranged to monitor the types of motors described above. Figure 8A shows a profile development logic module 503 as described above, which 25 receives terminal voltage (V), back EMF (e) and load current (I) signals from a switching bridge and motor 801 being tested. The motor 801 is driven by a power supply 803 and switching bridge 4 and loaded by a generator 820 and a load 805. According to this embodiment, the load is a variable resistive load to enable the motor to be tested under different load conditions. It will be 30 understood that different loads may be used to test the motor. According to this embodiment, the load is adjusted manually to drive the motor into a range of different load conditions. This enables motor performance characteristics to be developed for different load currents. Alternatively, the load Received at IPONZ 6 December 2010 17 805 may be adjusted automatically using a control system that is arranged to vary the load applied to the motor. It will also be understood that the power supply 803 may be a fixed power supply 5 or a variable power supply. Again, the power supply may be varied manually or through a control system that is arranged to adjust the power supply output. The V, e and I values obtained from the switching bridge and motor under test are used to develop a motor performance parameter (R) as described above. 10 The motor performance parameter R is communicated to a monitoring module 807. The monitoring module 807 also receives the load current (I) signal as a further input. The monitoring module 807 is also in communication with the storage module 505, which as described above stores R values of the motor for a set of load current (I) values. For example, the R and I values may be stored as 15 a look up table, best fit equation or in any other suitable format which enables a profile to be stored and its associated values to be retrieved. According to this embodiment, the R and I values are stored in the storage module as a benchmark profile. That is, the profile stored of R vs I is a preferred, 20 ideal or expected R/l profile that the majority of motors of the type being monitored should exhibit. The benchmark profile may be created by testing a number of motors to develop a number of profiles and then taking the average of those profiles to create the benchmark profile. Alternatively, the benchmark profile may be developed based on a set of desired motor performance 25 characteristics related to a desired quality of motor performance. The monitoring module receives an R value from the profile development logic module for a specific load current that is applied to the motor being tested. This same load current is used by the monitoring module to retrieve the expected R 30 value from the storage module. That is, the monitoring module compares the actual R value from the motor under test with the benchmark profile to compare the desired R value from the profile for the specific load current used in the test with the actual measured R value. The monitoring module 807 detects whether Received at IPONZ 6 December 2010 18 there is a difference between the actual R value and the desired R value from the benchmark profile and provides an output accordingly. The output 808 of the monitoring module may be in one or more of a number of 5 different forms (809, 811, 813, 815, 817). For example, the output may be a simple indication showing the numerical or percentage difference between the actual and benchmark R values. 10 According to a further example, the monitoring module may determine the difference between the measured and benchmark R values and output a signal based on whether the difference is above or below a defined threshold value. The output signal may identify one or more of: a motor performance parameter 15 value; a load current applied to the motor; an error value based on the determined difference; the threshold value; the benchmark profile; data identifying the motor being monitored; data identifying when the benchmark profile was created; data identifying when the motor was monitored. 20 The output signal may be in the form of an audio and/or visual signal. The audio signal (811) may be, for example, an alarm signal that is output from an audio output, such as a speaker for example. Alternatively, a recorded warning signal may be output indicating that the threshold has been reached or 25 exceeded, for example. The visual signal (809, 813) may be in the form of a visual report, chart, table or graph that identifies one or more of the measured, benchmark and/or difference values. Also, the visual signal may be a flashing light, coloured light, or displayed 30 worded message to indicate the threshold has or has not been exceeded, or is close to being reached. The visual signals in the form of a visual report, chart, table or graph may, for example, be printed out on a printer (813), displayed on a display device (809), Received at IPONZ 6 December 2010 19 communicated to an external device (817) for later retrieval, or stored in a storage module (815), such as a database, for example. The motors may be monitored remote from the mobility vehicle, i.e. after they 5 have been detached from the mobility vehicle, such as, for example, after the motor has been manufactured or assembled, or after it has been removed from the mobility vehicle due to a reported fault. Alternatively, the motor may be monitored while it is attached to the mobility vehicle, for example, to allow the motor to be tested while the mobility vehicle is being serviced. 10 Figure 8B shows a block functional diagram of a motor performance monitoring system which is arranged to monitor the types of motors described above. Figure 8B shows a profile development logic module 503 as described above, which receives terminal voltage (V), back EMF (e) arid load current (I) signals from a 15 switching bridge 4 and motor 801 being tested. The motor 801 is driven by a power supply 803 and switching bridge 4 and loaded by a generator 820 and a load 805. According to this embodiment, the load is a variable resistive load to enable the motor to be tested under different load conditions. It will be understood that different loads may be used to test the motor. 20 According to this embodiment, the load is adjusted manually to drive the motor into a range of different load conditions. This enables motor performance characteristics to be developed for different load currents. Alternatively, the load 805 may be adjusted automatically using a control system that is arranged to 25 vary the load applied to the motor. It will also be understood that the power supply 803 may be a fixed power supply or a variable power supply. Again, the power supply may be varied manually or through a control system that is arranged to adjust the power supply output. 30 The V, e and I values obtained from the switching bridge and motor under test are used to develop a motor performance parameter (R) as described above. The motor performance parameter R is communicated to a storage module 8G? Received at IPONZ 6 December 2010 20 505 along with the load current value. The storage module stores the profile of the motor as described above for specific load current values over time. A monitoring module 819 is in communication with the storage module 505, 5 which as described above stores R values of the motor for a set of load current (1) values. For example, the R and 1 values may be stored as a look up table, best fit equation or in any other suitable format which enables a profile to be stored and its associated values to be retrieved. 10 According to this embodiment, the motor performance monitoring system is arranged to monitor the performance of one or more motor performance parameters of a motor under test over time. The test may be used to develop a benchmark profile for use in the earlier described embodiment Also, the test may be used to develop quality control data for motors. For example, the test 15 data may be used to determine the expected operating life for certain motor types. The operating life may be based on determining how long It takes for a developed motor performance parameter to change over time such that it falls outside of a desired operating threshold. 20 The monitoring module 819 monitors the stored profile values of the motor being tested. A set of rules are utilised by the monitoring module to determine whether the developed profile is varying above a defined threshold for the set test parameters. For example, the monitoring module may use a set of rules to detect how much the R value is varying over time for a preset load current. If the 25 monitoring module detects that the R value has varied above a defined threshold value (an absolute value or percentage value, for example) before a set period of time has elapsed, an output is produced to indicate this finding. The output may be used to determine whether newly manufactured motors are within quality control thresholds. 30 Further, the above described system may be used to test motors that exhibit operating faults. For example, the motor may be tested by this monitoring system to determine whether the problem lies with the developed performance parameters of the motor. Received at IPONZ 6 December 2010 21 It will be understood that the motor may also be tested under varying load conditions or power supply conditions in the same manner as described with reference to the embodiment shown in Figure 8A. 5 It will be understood that the output 821 from the monitoring module of this embodiment may be the same as discussed with reference to the system described in Figure 8A (809, 811, 813, 815, 817). 10 It will be understood that the embodiments of the present invention described herein are by way of example only, and that various changes and modifications may be made without departing from the scope of invention. Received at IPONZ 6 December 2010 22 </div>

Claims

<div class="application article clearfix printTableText" id="claims"> CLAIMS

1. A method of controlling at least one motor in a motorised mobility vehicle, wherein the motor is part of a drive circuit for mobilising the mobility vehicle, the 5 method including the steps of: utilising a stored profile of a motor performance parameter to develop a compensation term for controlling the motor, wherein the stored profile is of a resistance based variable associated with the motor as a function of a further variable and 10 dynamically updating the compensation term when the mobility vehicle is in use.

2. The method of claim 1 further including the steps of: storing the performance parameter profile of the motor, developing the further variable by developing a load current of the motor, 15 developing the compensation term based on the stored profile and the developed load current, and applying the compensation term to the motor.

3. The method of claim 2, wherein the performance parameter profile is a 20 resistance based profile.

4. The method of claim 3, wherein the resistance based profile is a motor electrical resistance profile for varying load currents. 25

5. The method of claim 2, wherein the motor is one of a permanent magnet or shunt wound motor.

6. The method of claim 2, wherein the motor is a DC brush motor. 30

7. The method of claim 2, wherein the compensation term is updated continuously.

8. The method of claim 2, further including the step of dynamically updating the compensation term within a millisecond time frame. Received at IPONZ 6 December 2010 23

9. The method of claim 2, further including the step of constantly sensing the load current and dynamically updating the compensation term based on the sensed load current. 5

10. The method of claim 2, further including the step of developing the load current in real time to generate a real time compensation term to be applied to a motor control circuit for the motor. 10

11. The method of claim 2, wherein the compensation term compensates for the internal resistance of the motor.

12. The method of claim 11, wherein 100% of the compensation term is applied to the motor during all levels of motor loading. 15

13. The method of claim 11, wherein a portion of 100% of the compensation term is applied to the motor as the levels of motor loading vary.

14. The method of claim 13, wherein a reduced compensation term is applied 20 as the motor loading increases.

15. The method of claim 11, wherein the stored profile is shaped by current.

16. The method of claim 11, wherein the compensation term is shaped by the 25 stored profile.

17. The method of claim 11, wherein the compensation term is used to adjust the power applied to the motor. 30

18. The method of claim 2, further including the step of applying the compensation term as a proportional control term.

19. The method of claim 2, further including the step of applying the compensation term as an integral control term. Received at IPONZ 6 December 2010 24

20. The method of claim 2, wherein the mobility vehicle is one of a power wheelchair and mobility scooter. 5

21. The method of claim 2, wherein the method controls two or more motors forming part of a differential steering mechanism of the mobility vehicle and each motor has a separate compensation term applied to it.

22. The method of claim 2, further including the step of repeatedly updating 10 the profile of the motor while the motor is in motion.

23. The method of claim 22, further including the step of updating the profile of the motor based on a back EMF method. 15

24. The method of claim 23, wherein the back EMF method includes the step of developing the compensation term based on the developed load current.

25. The method of claim 23, wherein the back EMF sampling method includes the steps of: 20 developing the terminal voltage across the motor, the load current and the back EMF, and developing the compensation term based on the developed terminal voltage, load current and back EMF.

26. The method of claim 25, wherein the back EMF is developed after the 25 motor is turned off for a period of time.

27. The method of claim 26, wherein the period of time is pre-determined or based on a stored algorithm. 30 28. The method of claim 22, further including the step of determining whether the motor is being operated under a high load, and upon a positive determination, not updating the profile.

Received at IPONZ 6 December 2010 25

29. The method of claim 22, further including the step of updating the profile of the motor during servicing or repair of the mobility vehicle.

30. The method of claim 22, further including the step of updating the profile 5 of the motor during normal use of the mobility vehicle.

31. The method of claim 30, further including the step of updating the profile without affecting the operation of the motor during the update. 10

32. A control system in a motorised mobility vehicle, the control system arranged to control at least one motor wherein the motor is part of a drive circuit for mobilising the mobility vehicle, the control system including: a compensation term development module arranged to utilise a stored profile of a motor performance parameter to develop a compensation term for controlling the 15 motor, wherein the stored profile is of a resistance based variable associated with the motor as a function of a further variable and dynamically update the compensation term when the mobility vehicle is in use.

33. The control system of claim 32 further including: 20 a storage module arranged to store the performance parameter profile of the motor, a load current development module arranged to develop the further variable by developing a load current of the motor, the compensation term development module arranged to develop the 25 compensation term based on the stored profile and the developed load current, and a control module arranged to apply the compensation term to the motor.

34. The control system of claim 33 further arranged to perform the method of 30 any one of claims 3 to 31.

35. A method of controlling at least one motor in a motorised mobility vehicle substantially as herein described with reference to the accompanying figures. Received at IPONZ 6 December 2010 26

36. A control system in a motorised mobility vehicle substantially as herein described with reference to the accompanying figures. DYNAMIC CONTROLS / By their Attorneys ELLffc TERRY P5/1/6143 </div>